In order for it to be possible to handle the load on a truck effectively, load-handling equipment is necessary. Examples of such equipment is tipping gear and cranes. Also common are hook loaders, refuse-handling units, rotating cement mixers, flushing units and air compressors for loading or unloading bulk loads.
In order to utilize the driving power of the vehicle engine to drive the load-handling equipment, a power take-off is required. The driving power from the power take-off can be transmitted mechanically via a either propeller shaft or belts, or hydraulically using a hydraulic pump that is mounted on the power take-off.
Power take-offs are divided into coupling-independent and coupling-dependent power take-offs. The speed and power of the coupling-independent power take-offs follow the vehicle engine irrespective of whether the vehicle is being driven or is stationary. Coupling-independent power take-offs are suitable for load handling equipment which is used when the vehicle is being driven, for example refuse-handling units, cement mixers, refrigerating/freezing units and snowplows.
The coupling-independent take-offs can be mounted on the engine of the vehicle or mounted between the engine and gearbox of the vehicle but in front of (on the engine side) the disk clutch that is arranged between the engine and the gearbox.
Automatic gearboxes of the automated stage-geared gearbox type have become increasingly common in heavy-duty vehicles as microcomputer technology has further developed, making it possible, with a control computer and a number of actuators, for example servo motors, to precision-regulate engine speed, engagement and disengagement of an automated disk clutch between the engine and the gearbox and also the internal coupling means of the gearbox in such a way and in relation to one another that gentle shifting is always obtained at the correct engine speed.
The advantage of this type of automatic gearbox compared with a conventional automatic gearbox constructed with planetary gear stages and with a hydrodynamic torque converter on the input side is on the one hand that, especially as far as use in heavy-duty vehicles is concerned, it is more simple and robust, and can be manufactured at a considerably lower cost than the conventional automatic gearbox. On the other hand, that it has higher efficiency, which also means lower fuel consumption.
Traditionally, in the abovementioned types of automated stage-geared gearbox, the following happens when the driver of the vehicle wishes to engage a coupling-independent power take-off, equipped with a disk clutch for engaging/disengaging the power take-off, in order, for example, to drive a cement mixer arranged on the vehicle. Since vehicle's equipped with such gearboxes usually do not have a disk clutch pedal, the driver has to start by putting the gearbox in neutral position by means of a gear selector arranged in the vehicle and then insure that the engine goes to its idling speed in order to minimize (as far as possible) wear on the disk clutch of the power take-off. An alternative is to stop the engine completely, which the driver is compelled to do in cases where the engaging/disengaging device of the power take-off is of the claw coupling type. With a claw coupling, the engine must be stationary in order to avoid the claw coupling being damaged and scraping noise from occurring. The next step is that the driver engages the power take-off by means of a control arranged in the vehicle for controlling the power take-off. If the engine has been stopped, the driver must then restart the engine in this state. Finally, the driver adjusts the rotational speed of the power take-off by selecting the correct engine speed. The latter operation is normally carried out by means of a throttle control arranged in the vehicle.
The driver of a vehicle with a power take-off of previously-known design has to carry out a number of steps before the power take-off can ultimately be activated. This takes time, and may cause handling problems for the inexperienced driver.
A need therefore exists in a vehicle equipped with a coupling-independent power take-off and an automated stage-geared gearbox to simplify operations for the driver of the vehicle when he wishes to use the coupling-independent power take-off of the vehicle.